Many extracorporeal therapeutic procedures have in common the need to remove blood from the body and then return it after processing. These therapies include intermittent treatments (e.g. daily or thrice weekly) such as hemodialysis, hemofiltration, and hemapheresis, as well as a variety of similar but continuous procedures (such as continuous venovenous hemodialysis, hemofiltration and combinations thereof, and extracorporeal membrane oxygenation).
Accidental disconnection of these devices can lead to blood loss, especially at the high flow states typical for mechanically pumped renal replacement therapies. At blood flows of over 400 ml/min, undetected disconnection of returning blood could thus lead to multiple liters of hemorrhage in just a few minutes. This would cause profound illness, with the hemodynamic consequences of low blood pressure, reduced oxygen delivery to the vital tissues, risk of needing blood transfusion, and could result in myocardial infarction, stroke or even death.
Unfortunately, the prior methodology to detect disconnections is not ideal, and tragic complications still occur. The rate of blood loss is so high that it can be severe before medical staff might notice the hemorrhage, and often the patients are so ill that they might not feel or be able to communicate the catastrophic circumstance.
The prior art has addressed this potentially fatal extracorporeal complication by a variety of pressure and air-detector sensors that monitor the blood tubing. The success or lack of success from these approaches depends on whether the tubing disconnection occurs at the tubing segment carrying blood away from the patient (known as the “arterial” tubing) as opposed to the portion returning the processed blood to the body (the “venous” tubing). In the former circumstance, the arterial disconnection disrupts the flow of blood to the pump, which is detectable by virtue of air being pulled into the system or by a change in the relatively high pressure profile within the tubing. Thus, various rapid alarm states typically alert the medical staff to remedy hemorrhage from the disconnection, hopefully before significant quantities of blood are lost. While imperfect, those arterial disconnection detection methods are far more effective than those that attempt to sense venous disconnections. Those scenarios continue to be fraught with great risk of harm, despite safeguards that are universally required and built into the therapeutic medical devices.
The difficulty in detecting disconnections of that portion of the extracorporeal device and/or tubing that returns blood to the patient arises from the conceptual basis of the current technology. All commercial devices sense disconnections based on the pressure profile of the returning blood. Typically the tubing's intraluminal pressure is mechanically and continuously measured by use of a transducer connected to the blood's flow path (e.g. the tubing or specialized cuvettes). Disconnection would be sensed by a fall in the intraluminal tubing pressure of the blood being returned to the patient. Unfortunately, this approach is problematic, and thus not ideal, due to the pressure profiles inherent to extracorporeal therapies: The preferred embodiment of those medical devices is to have the returning pumped (venous) blood be in a low-pressure system. In fact, the pressure within the vein to which the treated blood returns is ideally much less than 50 mm Hg, often less 15 mm Hg. This low range of pressure within the patient's vasculature (effectively resisting the return of the blood to the body's vein) is often much less than the high pressure state within the long tubing carrying the pumped blood. Use of a needle (or catheter) at the end of the tubing in order to gain entry to the vein adds additional resistance, further raising the “venous” pressure profile to levels typically over 100 mg Hg and as high as 300 mm Hg. Thus, the pressure contributed by the patient's vein may be a small fraction of the total pressure within the return side of the extracorporeal tubing. Should the venous needle fall out, or be disconnected for example, the resultant drop in pressure can be such a small percent of the total pressure that it is undetected by the alarm circuitry.
The industry has responded to this problem by making the pressure monitor more sensitive to decreases in pressure; however, current methodologies are by necessity a compromise. Too great a sensitivity leads to false alarms as there are often mild fluctuations in pressure in the venous tubing such as those due to bends or kinks in the tubing, changing positions in the patient or patient's extremities. Too low a sensitivity avoids false alarms but allows more disconnections to be undetected. Furthermore, as medical advances lead to improvements in access to the body's vasculature (e.g. better arteriovenous fistulas or grafts), there will be even less resistance afforded by those structures: thus, an even smaller pressure drop would need to be detected by the conceptually unsatisfactory pressure-drop methodology.
The prior art also includes many inventions and devices that monitor a patient's electrical bioimpedance. Those methods share the feature that an electrical current is applied from an external generator, and pass through the patient using a variety of configurations of transmitting and sensing electrodes. Many such devices are marketed for the purposes of detecting changes in body composition, by virtue of altered impedance. Indeed, some such devices are sold for extracorporeal therapies as a means of guiding the medical prescription, and changes in impedance are used as an index of water and solute removal. None of those prior patented and marketed devices were designed to detect loss of the continuity of the externally generated current (or the resultant change in impedance) as a means of sensing a disconnection.
U.S. Patent Application No. US 2003/0195454 to R. Wariar, J. Han, G. Lamberson, T.P. Hartranft and T. Falkvall describes a new embodiment of bioimpedance technology to detect an extracorporeal device disconnection. In their preferred embodiment, they use an external current generator to establish an electrical circuit via the arterial and venous limbs of the tubing; changes in impedance would be interpreted as a disconnection, triggering an appropriate alarm condition.
However, the older bioimpedance technology as well as the more recent variation proposed by Wariar et al. (US 2003/0195454) are seriously flawed for routine use in patients, in that all those approaches by necessity apply an external current to (and through) the blood and body. The two major detriments to the external current generator approach are: 1) the safety concerns from any external power supply, or malfunctions thereof, directly energizing the extracorporeal blood; and 2) the possible detrimental effects of electrical currents on therapeutic electrical devices implanted in the patient (e.g. life sustaining pacemakers, automated implanted defibrillators) or used to monitor critically ill patients (e.g. intensive care unit hemodynamic monitors, external pacemakers, ventilators). Indeed the topic of even trivial electrical leaks from medical apparatuses into patients has been of grave concern in the literature and manufacturing industry.
The following patents are incorporated herein by reference: U.S. Patent Application No. 2003/0195454 and U.S. Pat. No. 6,979,306.
Accordingly since significant morbidity or mortality can result from hemorrhage when extracorporeal therapeutic devices incorporating blood pumps are accidentally disconnected from patients, there is a need in the art for adequate detection devices. Unfortunately, the current art is inadequate. Accordingly, there is a need in the art for systems and methods for detection of disconnection of a device, such as dislodgment of a device during medical treatments or therapies that do not rely on pressure or apply external currents.